Magnesium-lithium-sodnjm grease



Filed Dec. 13, 1952 FIGURE-I M9 NuLi HOURS AT 250F.

E r 1c 0. ForsTer Znventor United States atent IMAGNESIUM-LITIilIUM-SODIUM GREASE COMPOSITION Eric" 0. Forster,Hillside, N. 3., assignor to Essa Research and Engineering Company, acorporation of Delaware Application December 13, 1052, Serial No.325,837

5 Claims. (Cl. 252-40) This invention relates to lubricating greasecompositions and particularly to improved magnesium grease compositionswhich have excellent heat stability properties. More particularly theinvention relates to a heat stable magnesium grease compositioncontaining the magnesium, lithium, and sodium soaps of fatty acids.

Magnesium base greases are well known in the art of lubricating greasemanufacture. They are characterized by excellent appearance and by theirresistance to shear breakdown. It has been found, however, thatmagnesium base greases are somewhat lacking in stability properties atsustained high temperatures. When utilized for the lubrication of movingmetal parts at high temperatures for long periods of time theseotherwise excellent lubricants have been found to harden to anundesirable extent and to allow oil to separate. This combination of atendency to harden and to separate oil is an u-ndersirable one and manyattempts have been made to modify magnesium base greases to remove it.

On line of research in this direction has been the in corporation ofmetallic soaps, such as sodium soaps, potassium soaps and the like. Thishas not been satisfactory in that while the addition of these soapsdecreases the tendency of the magnesium grease to harden, it increasesthe amount of oil separation under conditions of sustained hightemperatures.

It has now been found and forms the object of this invention that theincorporation of minor amounts of both a sodium soap and a lithium soapin a magnesium base" grease results in a composition that has theexcellent structure stability and appearance of the magnesium greases ofthe prior art and in addition removes their tendency to become hard andto separate oil under conditions of sustained high temperature. Thiscombination of properties makes these new grease compositions extremelyuseful in lubrication applications such as in the sealed bearings ofelectric motors, railroad anti-friction bearings, and automotivebearings. The compositions of this invention demonstrate a combinationof desirable properties which are surprising and unexpected whencompared with the results of incorporating either sodium or lithiumsoaps alone in a magnesium base grease.

The greases of this invention are prepared by thickening to a greaseconsistency a lubricating oil base stock with a mixture of themagnesium, lithium and sodium soaps of any of the Well known fatty acidsfamiliar to lubricating grease makers. The greases of invention areprepared by the methods of manufacture familiar to the art and nospecial problems arise in their preparation. Care must be taken only toprepare the most insoluble soap first, followed by the lesser solubleand most soluble soaps in that order.

Briefly, the preparation involves the thorough admixture of. the fattyacids used in a portion of the mineral oil base and the application ofheat until a homogeneous mixture is obtained. A slurry or solution ofthe metallic base usually in the form of hydroxide is then added and'ice the mixture heated to dehydration. temperatures. On completion ofdehydration the total mixture is heated'to about 300 F., the balance ofthe mineral oil added and the final product cooled without stirring.

The lubricating oil chosen as the base for the grease compositions ofthis invention may be any of the mineral oil distillates known to theart. It should be remembered that the oil chosen for the grease baseshould be selected from those which. would perform the lubrication if anoil alone could'be used.- Parafiinic or naphthenic distillates havingviscosities within the range of from to 1000 SUS, preferably 40 to 250SUS at 210 F. may be utilized as the base for these improved magnesiumgreases. The lubricating oil constituent of these compositions may alsobe selected from a great number of the synthetic lubricants which arerapidly becoming important in the lubricating art. Exemplary of thesesynthetic lubes are the long chain esters, esters of dibasic acids suchas sebacic and adipic acid esters, polymerized hydrocarbons such aspolyolefins, polymerized cracked wax, etc., alkylated aromatics,polyglycols, polyglycol ethers, polyglycol esters, polyglycol etheresters, formals of hydroxyl-conmining compounds, etc.

As was stated above there is nothing critical in the fatty acid used toform the thickeners for these new grease compositions. The acid chosenmay be selected from a great number of commercially available fattyacids which include stearic acid, oleic acid, hydroxy stearic acid,bydrogenated fish oil acid, beef fat, tallow, the unsaturated glyceridesof various fatty acids or mixtures of the above 1 in any proportion. Theacids may be used with or without plasticizers such as the polyethyleneglycols and the like.

The thickening agent of the greases of invention consists of a mixtureof the magnesium, lithium and sodium soaps of the above mentioned acids.The ratio of the three soaps used will vary from about 5 to l to 1 molsof magnesium, lithium and sodium soaps, respectively, to about 1 to 5 to5 mols. The preferred compositions of the invention will contain aboutone-half molar proportion of lithium and sodium soaps to each mol ofmagnesium soap.

The amount of thetotal soap mixture that is utilized in preparing thegreases will depend upon the consistency desired in the final product.Ordinarily from about 5.0% by weight to about 30.0% will be used withfrom 10.0% to 25.0% by weight of the total mixture being especiallypreferred.

The instant invention will be more clearly explained by reference to thefollowing representative examples.

EXAMPLE I Formulation Ingredients: Weight percent Hydrogenated fish oilacids 22.00 Magnesium hydroxide 4.15 Lithium hydroxide 0.70 Sodiumhydroxide 1.00

Mineral lubricating oil (70 SUS/210'? F.) 72.15

Preparation The total charge of the hydogenated fish oil acids andone-third of the mineral oil were mixed and heated until a homogeneoussolution was obtained. An oil slurry of the magnesium hydroxide was thenadded and the magnesium soap allowed to form. Thereupon an aqueoussolution of lithium hydroxide was added and the lithium soap formed.Upon completion of this reaction an aqueous solution of the sodiumhydroxide was added and the sodium soap was prepared. The" total mixturewas then heated to 240 F. and dehydrated. After all the water was drivenoff the temperature was raised to 300 F. and the remainder of themineral oil was added gradually with stirring. Upon completion of theaddition of the mineral oil the product was cooled without furtherstirring.

EXAMPLE II Formulation Ingredients: Weight per cent Hydrogenated fishoil acids 20.00 Magnesium hydroxide 4.15 Lithium hydroxide 1.40

Mineral lubricating oil (70 SUS at 210 F.) 74.45

10 penetrations were again taken.

Preparation This composition was prepared as in Example I except that nomagnesium or lithium soaps were formed.

The grease compositions prepared as described above were tested for hightemperature stability by placing samples in an oven heated at 250 F. Thesamples were subjected to this high temperature for 500 hours. At statedintervals during the test period samples were subjected to themicro-penetration test and after 500 hours micro- The samples were alsothen examined for oil separation and appearance. Results of these testsshowing the outstanding advantage of the compositions of invention areset out in Table I below.

TABLE I.-HIGH TEMPERATURE GREASE STABILITY 500 HRS. OVEN TEST AT 250 F.

Preparation This composition was prepared the same as in Example Iexcept that no sodium soap was prepared.

EXAMPLE III Formulation Ingredients: Weight per cent Hydrogenated fishoil acids 20.00 Magnesium hydroxide 4.15 Sodium hydroxide 1.42 Minerallubricating oil (70 SUS at 210 F.) 74.43

Preparation This composition was prepared as in Example I except that nolithium soap was formed.

EXAMPLE IV Formulation Ingredients: Weight per cent Hydrogenated fishoil acids 20.00 Magnesium hydroxide 8.30 Mineral lubricating oil (70 SUSat 210 F.) 71.70

Preparation This composition was prepared as in Example I except that nolithium or sodium soap was prepared.

EXAMPLE V Formulation Ingredients: Weight per cent Hydrogenated fish oilacids 10.00 Lithium hydroxide 1.40 Mineral lubricating oil (70 SUS at210 F.) 88.60

Preparation This composition was prepared as in Example I except that nomagnesium or sodium soap was formed.

EXAMPLE VI Formulation Ingredients: Weight per cent Hydrogenated fishoil acids 14.00 Sodium hydroxide 2.00

Mineral lubricating oil (70 SUS at 210 F.) 84.00

These results are also shown pictorially in the accompanying drawing. Inthe drawing the micro-penetration of the samples are plotted against thenumber of hours subjected to the test temperature. It is graphicallyshown in the drawing that whereas the composition of invention remaineduniformly stable for the duration of the test, the greases of thecomparative examples softened to a great extent with subjection to thetest temperature.

The lubricating grease compositions of this invention have been found tobe compatible with various of the well known additive materials whichmay be included. There may be blended with these compositions suchmaterials as antioxidants, tackiness agents, color improvers and thelike without detracting from the desirable characteristics of thecompositions.

To summarize briefly this invention relates to improved magnesiumgreases which consist essentially of a lubricating oil base stockthickened to a grease consistency with a combination of the magnesium,lithium and sodium soaps of fatty acids. The total amount of soap willbe dependent upon the consistency desired in the final product but willpreferably vary from about 10.0% to about 25.0% by weight based on theweight of the total composition. The proportion of the component partsof the total mixture may vary from about 0.5 to 5 mols of lithium andsodium soap per mole of magnesium. The preferred embodiment, however,contemplates the use of one mol of lithium soap and one mol of sodiumsoap for two mols of magnesium soap to thicken to a grease consistency amineral oil distillate having a viscosity from 35 to 1000 SUS at 100 F.The greases are prepared by forming first the magnesium soap, then thelithium soap, and finally the sodium soap in a mineral oil, heating toabout 300 F. and then cooled without stirring.

What is claimed is:

1. A lubricating grease composition which consists essentially of alubricating oil base stock containing combined therein a grease formingamount of a mixture of magnesium, lithium, and sodium soaps of highmolecular weight fatty acids, said mixture containing a molar ratio ofmagnesium to lithium to sodium soaps of from 5:1:1 to 1:5:5.

2. A composition according to claim 1 wherein there is present from 5.0to 30.0% by weight of the total soap mixture.

3. A composition according to claim 1 wherein the lu- 5 bricating oilhas a viscosity at 210 F. within a range of from 35 to 1000 SUS.

4. A lubricating grease composition consisting essentially of a minerallubricating oil base stock thickened to a grease consistency with fromabout 10.0% to 25.0% by weight of a mixture of soaps comprising about 2molar proportions of a magnesium soap with about 1 molar proportion oflithium soap and about 1 molar proportion of sodium soap.

5. A process for the preparation of lubricating greases which comprisesthe steps of forming a magnesimn soap in a mineral lubricating oil, thenforming a lithium soap and a sodium soap respectively, heating the totalmixture to above the transition point of the soaps, adding additionalmineral oil, and then cooling the heated mixture.

References Cited in the file of this patent UNITED STATES PATENTS2,293,052 Earle Aug. 18, 1942 2,397,956 Fraser Apr. 9, 1946 2,409,950Meyer Oct. 22, 1946 2,417,429 McLennan Mar. 18, 1947 10 2,417,431McLennan Mar. 18, 1947 FOREIGN PATENTS 1,659 Great Britain Mar. 1, 1890

1. A LUBRICATING GREASE COMPOSITION WHICH CONSISTS ESSENTIALLY OF ALUBRICATING OIL BASE STOCK CONTAINING COMBINED THEREIN A GREASE FORMINGAMOUNT OF A MIXTURE OF MAGNESIUM, LITHIUM, AND SODIUM SOAPS OF HIGHMOLECULAR WEIGHT FATTY ACIDS, SAID MIXTURE CONTAINING A MOLAR RATIO OFMAGNESIUM TO LITHUMN TO SODIUM SOAPS OF FROM 5:1:1 TO 1:5:5.